—
At the start of spring and the onset of autumn, activities in the garden are greatly influenced by the soil temperature. Getting the timing right is crucial for successful gardening, and it all comes down to soil temperature.
—
As plant cells can only function within a narrow temperature range, it is crucial for plants to be exposed to temperatures within the optimal range to ensure healthy growth and development. Monitoring soil temperature is a valuable tool in ensuring that issues with pests and disease are kept at bay. It is also essential for the effective use of natural allies like beneficial nematodes. Soil temperature measurements come in handy in various situations. In this blog post, we explain what soil temperature is and why it matters. We explore how it affects plants, pests, diseases, and beneficial nematodes as biocontrol agents. Plus, we provide helpful tips for measuring soil temperature in your garden.
What is soil temperature, and why is it important?
Soil temperature is a measure of how warm or cold it is at a specific depth in the ground. Land heating is mainly caused by solar radiation. Soil temperature is not a constant value, but is rather influenced by various factors like color, slope, vegetation, moisture, and sunlight exposure. As a result, the warmth of the ground varies at different depths, with the upper layers typically being warmer than the deeper layers. Soil warms up and cools down more slowly than air. It takes several days of warm weather, both during the day and at night, to significantly raise soil temperature—not just one or two warm days in early spring.
Soil temperature affects various plant processes like nutrient and water absorption, growth, and crop development. The microclimate in your garden might not match the soil temperature you see on maps. Farmers and gardeners rely on soil temperature to determine the best time to plant their crops. Knowing the soil temperature also helps to decide when to release natural biocontrol agents like beneficial nematodes. To prevent frost damage to plants and protect beneficial nematodes, it's essential to monitor soil temperature closely.
How soil temperature affects plants
Plants can be harmed by temperatures that are too low or too high, which depends on the plant species. Low temperatures pose a challenge to the normal growth of plants, as they diminish the intensity of biological and chemical processes in the soil. Tomatoes, for example, tend not to germinate when temperatures are below 5°C or exceed 36°C, and they grow very slowly at 10°C. Being a warm-season vegetable, tomato seeds germinate best between 16°C and 29°C. Cool-season vegetables like lettuce, germinate best in temperatures between 4°C and 26°C, with a minimum temperature of 2°C.
Optimal temperatures facilitate chemical reactions that break down the seed coat and inform the seed that it’s all right for it to sprout. Soil temperature also affects photosynthesis. When some plants are exposed to low temperatures or chilling (1°C to 10°C), photosynthesis tends to be slow. Plus, when the soil temperature is below 7°C, plant roots face difficulty in absorbing water and soil nutrients efficiently. In contrast, optimal soil temperatures will favor a quick synthesis of more nutrients and consequently, a healthier growth.
How soil temperature influences pests and diseases
Extreme soil temperature in your garden can cause trouble. When plants are stressed by low or high soil temperatures, they become more susceptible to diseases and pests. Stressful conditions are also ideal for unfriendly organisms to thrive. For example, some plants are susceptible to damping-off when the soil temperature is low. Occasionally, when it becomes too hot, spider mite infestation can develop. Ensuring that you plant at the optimal soil temperature can keep pests and diseases at bay in your garden.
How soil temperature affects beneficial nematodes
Typically, beneficial nematodes are unable to survive temperatures below 0°C or above 37°C. Additionally, temperatures below 10°C to 15°C can limit their mobility. Beneficial nematodes are negatively impacted by temperatures above 30°C, diminishing their survival and pathogenicity. However, due to thermal adaptations from environments where they were isolated, some nematodes can thrive in cold regions with soil temperatures below 10°C to 15°C, while others may excel in hot semi-arid areas with temperatures ranging from 30°C to 35°C. The ideal soil temperature range for applying most beneficial nematodes is typically between 12°C to 30°C. Many nematodes are most effective in controlling pests within a soil temperature range of 20°C to 30°C.
Optimal soil temperature for nematode application
Ideal soil temperatures vary depending on the type of nematode. Here are the recommended soil temperature ranges for the most commonly used nematodes.
Nematodes | Minimum | Optimum range | Maximum |
(°C) | (°C) | (°C) | |
Steinernema feltiae | 8 | 15-25 | 30 |
Steinernema carpocapsae | 12 | 20-30 | 30 |
Heterorhabditis bacteriophora | 12 | 20-30 | 30 |
Measuring soil temperature in the garden
If you want to make accurate readings, you can easily check the soil temperature in your garden by using a soil thermometer. If you don't have one on hand, a meat thermometer can also do the trick.
Use a long screwdriver to dig a hole that is 10-15 cm deep in the garden area soil with a diameter comparable to your thermometer.
Insert the thermometer into the soil for 3 minutes. Shade the thermometer from sunlight if necessary.
Record the temperature.
The chosen sites for temperature measurement should accurately reflect the characteristics of the land (soil cover, slope, soil moisture, etc.) that will be utilized. Monitoring and understanding soil temperature is critical to a successful garden, both in terms of pest control, overall plant growth, and many other contexts.
Checking soil temperature is usually a simple and enjoyable task.
... ... ... ... ... ... ...
References
Hatfield, J.L., Prueger, J.H. 2015. Temperature extremes: Effect on plant growth and development. Weather and Climate Extremes, 10, 4-10.
Lorenz, O.A., Maynard, D.N. 1988. Knott's handbook for vegetable growers. John Wiley and Sons, New York. 630 p.
Ochner, T.E. 2008. Measuring soil temperature. In: Logsdon, S. Clay, D., Moore D., Tsegaye, T. (eds) Soil Science: Step-by-Step Field Analysis. pp. 235-251.
Tomalak, M., Pigott, S., Jagdale, G.B. 2005. Application technology. In: Nematodes as Biocontrol Agents. CABI, New York, NY, pp. 147-166.